The present invention relates to a multilayer sunshield lamination structure formed on a sheet of vitreous material, a glass sheet bearing said lamination structure as well as a multiple glazing incorporating such a glass sheet.
Sunshield lamination structures, to which the present invention relates, comprise at least one functional layer based on a material that reflects infrared radiation and at least two dielectric coatings, one of which is the first dielectric coating deposited directly onto the sheet of vitreous material and the other lies on the outside in relation to the functional layer or layers, each functional layer being surrounded by dielectric coatings. These different layers are deposited by reduced-pressure cathodic sputtering assisted by a magnetic field, for example, in a well known magnetron type device.
These sunshield laminations are used to form sun-protection glazings in order to reduce the risk of excessive temperature rise, for example, in an enclosed space with large glazed surfaces as a result of insolation and to thus reduce the power load to be taken into account for air-conditioning in summer. In this case, the glazing must allow the least possible amount of total solar energy radiation to pass through, i.e. it must have the lowest possible solar factor (SF or g). However, it is highly desirable that it guarantees a certain level of light transmission (LT) in order to provide a sufficient level of illumination inside the building. These somewhat conflicting requirements express the requirement to obtain a glazing unit with an elevated selectivity (S), defined by the ratio of light transmission to solar factor. These sunshield laminations also have a low emissivity, which allows a reduction in the heat loss through high wavelength infrared radiation. Thus, they improve the thermal insulation of large glazed surfaces and reduce energy losses and heating costs in cold periods.
The light transmission (LT) is the percentage of incident light flux, of illuminant D65, transmitted by the glazing. The solar factor (SF or g) is the percentage of incident energy radiation, which, on the one hand, is directly transmitted by the glazing and, on the other hand, is absorbed by this and then radiated in the opposite direction to the energy source in relation to the glazing.
These sunshield glazing units are generally assembled as double glazing units, in which the glass sheet bearing the lamination structure is joined to another glass sheet, with or without a coating, with the multilayer lamination structure located inside the space between the two glass sheets.
In some cases, it is often necessary to subject the glazing to a mechanical strengthening operation such as a thermal toughening of the glass sheet or sheets in order to improve its resistance to mechanical stresses. In the production process and shaping process of the glazing units there are some advantages in conducting these toughening operations on the already coated substrate instead of coating a substrate that has already been treated. These operations are conducted at a relatively elevated temperature, i.e. a temperature at which the, e.g. silver-based, infrared reflecting layer tends to deteriorate and lose its optical properties and its properties with respect to infrared radiation. In the case where the coated glass sheet has to undergo a thermal toughening operation, therefore, quite specific precautions must be taken to form a lamination structure that is able to undergo a thermal toughening or bending treatment, often referred to below by the expression “toughenable”, without losing its optical and/or energy-related properties, for which it is formed.
It is also desirable that the glazing units meet certain aesthetic criteria in terms of light reflection (LR), i.e. the percentage of incident light flux—of illuminant D65—reflected by the glazing, and reflected and transmitted colour. The market demand is for a glazing with low light reflection. The combination of a high selectivity with a low light reflection sometimes results in the formation of purple tints in reflection, which have very little aesthetic appeal.
To reduce the amount of heat that penetrates into the location through the glazing, the invisible infrared heat radiation is prevented from passing through the glazing by reflecting it. This is the role of the functional layer or layers based on a material that reflects infrared radiation. This is an essential element in a sunshield lamination structure. However, a significant portion of the heat radiation is also transmitted by visible radiation. To reduce the transmission of this portion of the heat radiation and go beyond eliminating the supply of energy by infrared radiation, it is necessary to reduce the level of light transmission.
The solution proposed by patent application WO 02/48065 A1 is to insert an absorbent layer, e.g. of TiN, into the lamination structure and to enclose this layer between two layers of transparent dielectric material. In this way, this document explains, the absorbent layer is not in contact with the glass, which limits the problems associated with the diffusion of oxygen and alkaline substance coming from the glass, in particular under the effect of heat when the glass must undergo thermal treatment, nor is it in direct contact with the silver, which limits the problems of deterioration of the silver layer caused by oxidation of the absorbent layer upon contact, in particular under the effect of the heat.
One of the problems results directly from what has just been stated, and that is that the absorbent layer oxidises in certain conditions, in particular during thermal treatment, and becomes more transparent, thus losing part of the reason for it being included in the lamination. Moreover, the level of oxidation of the absorbent layer will depend on the conditions of the thermal treatment, which means that it will be difficult to retain the properties of the lamination after toughening. To limit this effect, the above-cited document proposes to enclose the absorbent layer between two layers of silicon nitride or aluminium nitride.
In addition to the fact that the result is not completely satisfactory, the solution proposed by this document has the disadvantage of somewhat further complicating the lamination structures that are already complex in nature. In particular, this solution can require the use of a specific deposition zone with adjusted atmosphere right in the middle of a given dielectric to deposit the absorbent layer. Another disadvantage of the solution proposed by this document WO'065 is the difficulty in neutralising the tint provided by the absorbent layer inserted in the middle of a dielectric.
The invention relates to a multilayer sunshield lamination structure formed on a sheet of vitreous material comprising at least one functional layer composed of a silver-based material that reflects infrared radiation and at least two dielectric coatings, one of which is the first dielectric coating deposited directly onto the sheet of vitreous material and the other lies on the outside in relation to the functional layer or layers, each functional layer being surrounded by dielectric coatings, wherein said lamination structure, when deposited on an ordinary clear soda-lime float glass sheet 6 mm thick, has a solar factor SF of less than 45% and a light transmission LT of less than 70%, characterised in that the lamination structure is composed of an essentially metal absorbent material based on at least one of the following elements: Pd, Pt, Au, Ir, Rh, Ru, Os, Co, Ni, Cu, Cr, La, Ce, Pr, Nd, W, Si, Zn, Mo, Mn, Ti, V, Nb, Hf, Ta and alloys thereof arranged in the immediate vicinity of the functional layer or included in this functional layer.
The term “absorbent material” is understood to mean a material that absorbs a portion of the visible radiation, and of which the spectral absorption index k(λ) is higher than 1.9 on average, said average being calculated from three points of the visible spectrum located at 380, 580 and 780 nm. Spectral absorption index values are given in “Handbook of Chemistry and Physics”, 70th Edition, CRC Press, 1989-1990, E389-E404.
The absorbent material used in the invention is essentially in metal form. It may possibly also be doped with an element not included in the list, such as aluminium or boron, for example, for various reasons, in particular for ease of deposition in a magnetron device or ease of machining the targets.
It is known that silicon should properly be classed as a semimetal, but as silicon behaves like certain metals in various respects, it has been included in the present invention in the term “essentially metal absorbent material” to simplify matters.
The term “immediate vicinity” indicates that the absorbent material forms part of a layer arranged in direct contact with the functional layer or possibly separated from this by a very thin layer of sacrificial metal with a tendency to absorb oxygen or metal sub-oxide. Since the absorbent material is located in the immediate vicinity of the functional layer or is included in this functional layer, it can thus have a favourable effect on the reflection of infrared radiation and additionally benefits from the protective measures against oxidation intended for the material reflecting the infrared radiation.